Coloring compositions generally are mixtures of colorants (pigments, dyes, etc.) dispersed or dissolved in a carrier fluid. Hydrocarbon solvent-based coloring compositions, such as writing and marker inks, have traditionally been permanent inks. However, along with their desirable permanency, they present several undesirable qualities. The solvent systems utilized in these inks typically include such toxic hydrocarbons as toluene and xylene. Such components can lead to both disposal problems and consumer rejection due to a rising appreciation for the dangers of exposure to toxic chemicals and objection to the chemical odor.
Water-based coloring compositions present an attractive alternative to hydrocarbon-based coloring compositions, primarily because aqueous coloring compositions are less toxic and their odor less offensive than hydrocarbon-based coloring compositions. Water-based coloring compositions are generally made by a mixture of water and a colorant (e.g., a water soluble dye or pigrnent). While some water-based coloring compositions available in the form of marker inks have the desirable quality of good skin and textile fugitivity, they also exhibit the undesirable quality of washing off of the writing surface. Water-based writing and marker inks also tend to smear during application, in part because of long drying time. After being dispensed and dried, such inks are re-wettable and will again smear if later contacted with water. Some of these problems are surmounted by incorporating an acrylic resin, such as an alkali-soluble resin, into the coloring composition.
Coloring compositions are employed to mark on a wide variety of substrates. A commonly employed substrate is paper (or a paper-like material), which is produced in many qualities. In many respects, paper presents a superior writing surface. The surface of paper is generally smooth and even. Moreover, the porosity of paper assists the writing process by drawing the coloring composition into the paper matrix, promoting even application and smooth appearance. However, porous paper is not an ideal writing substrate for all applications. For example, many types of paper (e.g., newsprint, or the highly porous paper commonly employed in children's coloring books) are sufficiently porous to draw a coloring composition through the paper to create a mark on the surface opposite that desired, thereby rendering it difficult to employ both sides of a single sheet of paper. This is commonly referred to as "strike-through" of the ink. Moreover, inks which strike through (or bleed through) paper can actually leave marks on surfaces supporting the paper (such as succeeding sheets of paper in a book, clothing, firniture, and the like). Also, strike-through dulls or reduces the presentation of the color.
Efforts aimed at reducing drying time and strike-through of water-based inks have proven largely unsuccessful. Some commercially available inks reduce strike-through by incorporating additives which substantially increase the viscosity of the coloring composition. For example, hyperthermogelling inks incorporating a high amount of surfactants exhibit a phase change due to the evaporation of a given amount of water (e.g., U.S. Pat. No. 5,462,591). While such inks are useful for some applications (e.g., commercial printing presses), they are too viscous for use in common writing instruments, such as capillary markers with porous nibs.
In view of the foregoing problems, there exists a need for a coloring composition that is quick-drying and which exhibits limited or little strike-through when applied to porous papers such as coloring book paper. There is also a need for such compositions that are washable from skin and common fabrics. Furthermore, such compositions are needed which are suitable for use in common ink-based writing instruments (e.g., capillary markers). The present invention meets these needs and provides a low bleed coloring composition suitable for use in common ink-based marking instruments.